The goal of this project is fluorescently visualize potassium (K+) egress and extracellular accumulation at the cell surface. The development of this innovative technology has the potential to enable the large-scale spatiotemporal resolution of neuronal and glial cell activity. For this project, we are exploiting the presence of the cell's glycocalyx to attach potassium-sensitive fluorophores exactly where K+ accumulates and is reabsorbed by glia. There is one aim to this project: To synthesize a novel, near-IR K+ sensor that covalently modifies the glycocalyces of living cells to fluorescently detect and measure K+ efflux and accumulation. The completion of this aim will yield a transformative set of chemical-biological tools and methodologies to investigate the physiology and pathophysiology of K+ activity in neurons, glia, and potentially in living animals.